Field of the Invention
The invention relates to an undervoltage tripping device as an attaching module for a multipolar low-voltage switching device. The undervoltage tripping device includes an electromagnetic tripping mechanism for effectuating a tripping of the multipolar low-voltage switching device given a drop below a predeterminable voltage limit value. A rectifier bridge is provided and is powered by the multiphase power supply circuit and has a number of rectifier branches corresponding to the number of the phases of the multiphase power supply circuit. The branches power the electromagnetic tripping mechanism. The electromagnetic tripping mechanism effectuates an all-pole tripping of the multipolar low-voltage switching device given a failure of one of the phases. A corresponding monitoring circuit for detecting phase errors in a multipolar switching device is described in U.S. Pat. No. 3,242,383. The term low-voltage switching device specifically refers to a power switch such as an over-current circuit breaker.
Beyond this, Published, European Patent Application EP 0 802 552 A2 describes this kind of electrical switch which includes an electromagnetic undervoltage tripping device which is constructed as a magnetic circuit with a magnetic coil or tripping coil and a moving magnetic armature. The moving magnetic armature is mechanically coupled with a switching member of the electrical switch in such a way that the switching member is tripped and transferred into its off position when a monitored mains voltage of the supply network that is being protected drops below a prescribed limit value as a consequence of the opening of the magnetic circuit. A reclosing of the switching member given an undervoltage tripping device that is coupled to the electric switch is only possible if the magnetic circuit is reclosed, on one hand, and the monitored mains voltage exceeds the voltage limit value, on the other hand.
The undervoltage tripping device is customarily used in a unipolar or bipolar switching device and supplied by the monitored supply network in one or two phases. But the disadvantage of this type of monophase or biphase powering of the undervoltage tripping device is that, in the monitoring of a multiphase supply network with a tripolar or quadrupolar switching device, the undervoltage tripping device, which is already needed for safety reasons, is unreliable, at least when a phase that is not utilized for the voltage supply to the undervoltage tripping device fails.
It is accordingly an object of the invention to provide an undervoltage tripping device which overcomes the above-mentioned disadvantages of the prior art devices of this general type, in particular for a tripolar or quadrupolar overcurrent circuit breaker, which provides tripolar protection and can be built modularly with optimal ease as an inexpensive attaching part.
With the foregoing and other objects in view there is provided, in accordance with the invention, an undervoltage tripping device as an attachable module for a multipolar low-voltage switching device. The undervoltage tripping device contains an electromagnetic tripping mechanism for effectuating a tripping of the multipolar low-voltage switching device given a drop below a predeterminable voltage limit value. The electromagnetic tripping mechanism has a magnetic circuit with a spring-loaded armature and a trip coil including a number of winding portions corresponding to a number of phases of a multiphase power supply circuit. A rectifier bridge is provided and is powered by the multiphase power supply circuit. The rectifier bridge has a number of rectifier branches corresponding to the number of the phases of the multiphase power supply circuit. The rectifier bridge is connected to the electromagnetic tripping mechanism and the rectifier branches jointly power the electromagnetic tripping mechanism. The electromagnetic tripping mechanism effectuates an all-pole tripping of the multipolar low-voltage switching device given a failure of one of the phases of the multiphase power supply circuit. The rectifier bridge is a three-pulse bridge circuit, each of the winding portions of the electromagnetic tripping mechanism are disposed in one of the rectifier branches. The failure of at least one of the phases has an effect that a restoring force acting on the armature surpasses a holding power generated by the magnetic circuit.
The tripping device therein effectuates an all-pole tripping of the switching device given failure of only one phase.
The invention is thus based on the consideration that, when a three-pulse rectifier bridge circuit is utilized, given failure of only a single phase on the supply side on the alternating current side, the effective value of the current on the direct current side already drops in correspondence to the emerging gap in the direct current. If the direct voltage emerging on the direct current side of the three-pulse bridge circuit is applied as the supply voltage for the electromagnetic tripping mechanism of the undervoltage trip, the effective value of the supply voltage also drops as a result of an unbalancing of the rectifier branches within the bridge circuit conditional to the phase failure. The direct voltage of the multipolar or multiphase rectifier bridge circuit, which voltage is utilized to power the electromagnetic tripping mechanism of the undervoltage trip, thus directly replicates the failure of each individual phase of the monitored supply network and can therefore be used as a reliable trip criterion.
In the principal embodiment of the invention, the direct voltage which is generated by the rectifier bridge serves as a holding voltage for an armature which is situated in a magnetic circuit or magnetic system which is acted upon by a restoring force, which force opposes a holding power that is generated by the holding voltage. When the effective value of the holding voltage drops owing to an unbalancing of the rectifier bridge, the magnitude of the holding power is smaller than the magnitude of the restoring force, with the result that the armature lowers, bringing about the desired tripping. In a particularly expedient development, the functional principle is realized in that the tripping mechanism contains a U-shaped yoke with a coil body, which bears individual coil portions of the trip coils. The coil body is expediently subdivided into a number of adjacent chambers corresponding to the number of winding portions. The winding portions can also be wound over one another in a yoke bearing an unpartitioned, i.e. non-subdivided, coil body and separated from one another by insulating films.
The number of winding portions corresponds to the number of rectifier branches, which contain the individual winding portions in a series circuit with respective rectifier diodes. The electromagnetic tripping mechanism is thus expediently a trip relay that is constructed with a corresponding coil body, which can also be constructed small. The tripping mechanism so constructed can then be integrated with the rectifier bridge circuit in a housing, which can be utilized as an attaching module for the switching device.
The dropping resistor which is required for the electromagnetic tripping mechanism, particularly for its trip coils, can be realized by an individual ohmic resistor connected to the tripping mechanism on line side, or a number of subresistors corresponding to the number of rectifier branches. The dropping resistor, i.e. the corresponding dropping resistance value for the tripping mechanism, is expediently split into the individual phases in the rectifier branches in equal parts.
The specific advantage achieved by the invention is that, by powering an electromagnetic tripping mechanism by way of a tripolar rectifier bridge circuit, a multiphase undervoltage trip is provided, which effectuates an all-pole tripping of the connected switching device given failure of an arbitrary phase of the monitored supply network. The undervoltage trip so constructed is particularly suitable as an attaching module for a tripolar or quadrupolar overcurrent circuit breaker.
The undervoltage tripping device, in conjunction with a corresponding switching device or power switch, thus provides a reliable all-pole protection of a consumer that is connected to the corresponding supply network, regardless of which and how many phases of the supply network fail.
In accordance with an added feature of the invention, each of the rectifier branches has at least one diode with a cathode side and one ohmic resistor connected downstream from the diode on the cathode side. A total resistance value of the resistors in the rectifier branches corresponds to a dropping resistance value of the electromagnetic tripping mechanism.
In accordance with an additional feature of the invention, at least one diode is disposed in each of the rectifier branches, and the electromagnetic tripping mechanism has a dropping resistor connected to the diode connected in each of the rectifier branches.
In accordance with a further feature of the invention, the electromagnetic tripping mechanism has a yoke and a coil body supported by the yoke. The winding portions are disposed in the yoke.
In accordance with a concomitant feature of the invention, the coil body is partitioned into a number of chambers corresponding to a number of the winding portions.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an undervoltage tripping device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.